✨ Add strong type definition for fetch().json()

Closes uhyo#24

Author: aaditmshah

docs/diff/dom.generated.d.ts.md

@@ -11,5 +11,16 @@ Index: dom.generated.d.ts
  /// Window APIs
  /////////////////////////////
 
+@@ -2800,9 +2801,9 @@
+   readonly bodyUsed: boolean;
+   arrayBuffer(): Promise<ArrayBuffer>;
+   blob(): Promise<Blob>;
+   formData(): Promise<FormData>;
+-  json(): Promise<any>;
++  json(): Promise<JSONValue>;
+   text(): Promise<string>;
+ }
+ 
+ interface BroadcastChannelEventMap {
 
 ```

generated/lib.dom.d.ts

@@ -2802,9 +2802,16 @@ interface Body {
   arrayBuffer(): Promise<ArrayBuffer>;
   blob(): Promise<Blob>;
   formData(): Promise<FormData>;
-  json(): Promise<any>;
+  json(): Promise<JSONValue>;
   text(): Promise<string>;
 }
+//     readonly body: ReadableStream<Uint8Array> | null;
+//     readonly bodyUsed: boolean;
+//     arrayBuffer(): Promise<ArrayBuffer>;
+//     blob(): Promise<Blob>;
+//     formData(): Promise<FormData>;
+//     json(): Promise<any>;
+//     text(): Promise<string>;
 
 interface BroadcastChannelEventMap {
   message: MessageEvent;

lib/lib.dom.d.ts

@@ -0,0 +1,9 @@
+interface Body {
+  readonly body: ReadableStream<Uint8Array> | null;
+  readonly bodyUsed: boolean;
+  arrayBuffer(): Promise<ArrayBuffer>;
+  blob(): Promise<Blob>;
+  formData(): Promise<FormData>;
+  json(): Promise<JSONValue>;
+  text(): Promise<string>;
+}

tests/src/dom.ts

@@ -0,0 +1,7 @@
+import { expectType } from "tsd";
+
+const test = async (url: string) => {
+  const response = await fetch(url);
+  const json = await response.json();
+  expectType<JSONValue>(json);
+};

tests/tsconfig.json

@@ -1,12 +1,12 @@
 {
   "compilerOptions": {
     "target": "esnext",
-    "lib": ["esnext"],
+    "lib": ["esnext", "dom"],
     "module": "esnext",
     "moduleResolution": "node",
     "noEmit": true,
     "strict": true,
     "types": []
   },
   "include": ["./src/*.ts"]
-}
+}